U.S. patent application number 17/552667 was filed with the patent office on 2022-04-07 for resin composition, melt-forming material, multilayer structure, and agricultural film.
This patent application is currently assigned to MITSUBISHI CHEMICAL CORPORATION. The applicant listed for this patent is MITSUBISHI CHEMICAL CORPORATION. Invention is credited to Minako IKESHITA, Shintaro USUI.
Application Number | 20220106476 17/552667 |
Document ID | / |
Family ID | |
Filed Date | 2022-04-07 |
United States Patent
Application |
20220106476 |
Kind Code |
A1 |
USUI; Shintaro ; et
al. |
April 7, 2022 |
RESIN COMPOSITION, MELT-FORMING MATERIAL, MULTILAYER STRUCTURE, AND
AGRICULTURAL FILM
Abstract
A resin composition contains: (A) an ethylene-vinyl alcohol
copolymer having an ethylene structural unit content of 20 to 60
mol %; (B) a saponified ethylene-vinyl acetate copolymer having an
ethylene structural unit content of not less than 70 mol %; and (C)
a sorbic acid ester; wherein the sorbic acid ester (C) is present
in an amount of 0.00001 to 10 ppm based on the weight of the resin
composition. The resin composition is resistant to coloration.
Inventors: |
USUI; Shintaro; (Tokyo,
JP) ; IKESHITA; Minako; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MITSUBISHI CHEMICAL CORPORATION |
Tokyo |
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JP |
|
|
Assignee: |
MITSUBISHI CHEMICAL
CORPORATION
Tokyo
JP
|
Appl. No.: |
17/552667 |
Filed: |
December 16, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16838557 |
Apr 2, 2020 |
11230639 |
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17552667 |
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PCT/JP2018/043114 |
Nov 22, 2018 |
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16838557 |
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International
Class: |
C08L 29/04 20060101
C08L029/04; A01G 13/02 20060101 A01G013/02 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 22, 2017 |
JP |
2017-224609 |
Claims
1. A resin composition comprising: (A) an ethylene-vinyl alcohol
copolymer having an ethylene structural unit content of 20 to 60
mol %; (B) a saponified ethylene-vinyl acetate copolymer having an
ethylene structural unit content of not less than 70 mol %; and (C)
a sorbic acid ester; wherein the sorbic acid ester (C) is at least
one selected from the group consisting of methyl sorbate and ethyl
sorbate; and wherein the sorbic acid ester (C) is present in an
amount of 0.00001 to 10 ppm based on weight of the resin
composition.
2. The resin composition according to claim 1, wherein the
ethylene-vinyl alcohol copolymer (A) and the saponified
ethylene-vinyl acetate copolymer (B) are present in a weight ratio
(A)/(B) of 1/99 to 99/1.
3. A melt-forming material comprising the resin composition
according to claim 1.
4. A multilayer structure comprising a layer that comprises the
resin composition according to claim 1.
5. An agricultural film comprising the multilayer structure
according to claim 4.
Description
RELATED APPLICATION
[0001] This a divisional application of U.S. patent application
Ser. No. 16/838,557, filed on Apr. 2, 2020, which is a continuation
of International Application No. PCT/JP2018/043114, filed on Nov.
22, 2018, which claims priority to Japanese Patent Application No.
2017-224609, filed on Nov. 22, 2017, the entire contents of each of
which being hereby incorporated by reference.
TECHNICAL FIELD
[0002] The present disclosure relates to a resin composition
containing an ethylene-vinyl alcohol copolymer (hereinafter
referred to as "EVOH"), a melt-forming material produced by using
the resin composition, a multilayer structure, and an agricultural
film. More specifically, the present disclosure relates to a resin
composition excellent in coloration-suppressing effect, a
melt-forming material formed from the resin composition, a
multilayer structure including a layer formed from the resin
composition, and an agricultural film.
BACKGROUND ART
[0003] EVOH is excellent in transparency, gas barrier properties
such as oxygen barrier property, aroma-retaining property, solvent
resistance, oil resistance, and mechanical strength, and is formed
into films, sheets, bottles, and the like, which are widely used as
various packaging materials such as food packaging materials,
pharmaceutical product packaging materials, industrial chemical
packaging materials, and agricultural chemical packaging materials.
However, EVOH is disadvantageously poor in impact resistance,
flexural fatigue resistance, stretchability, thermoformability,
heat sealability, and gas barrier properties in a moisture or water
absorbed state.
[0004] A known approach to this disadvantage is to use a saponified
ethylene-vinyl acetate copolymer having an ethylene structural unit
content (hereinafter referred to as "ethylene content") of not less
than 70 mol % as an EVOH property-improving agent.
[0005] The saponified ethylene-vinyl acetate copolymer having an
ethylene content of not less than 70 mol % (hereinafter referred to
as "higher ethylene content EVOH") is a thermoplastic resin mainly
containing an ethylene structural unit and further containing a
hydroxyl group. The higher ethylene content EVOH is similar in
structure to ordinary EVOH, but has a higher ethylene content than
ordinary EVOH. Thus, the higher ethylene-content EVOH has different
properties from ordinary EVOH and, therefore, is generally regarded
as a resin different from ordinary EVOH.
[0006] PTL 1, for example, discloses a soil-covering film imparted
with excellent toughness by blending higher ethylene content EVOH
and ordinary EVOH in a specific blend ratio. PTL 2 discloses a
silage film imparted with thrust strength and tensile elongation
without deterioration in gas barrier property by blending higher
ethylene content EVOH and ordinary EVOH in a specific blend ratio.
Further, PTL 3 discloses that higher ethylene content EVOH is used
as a resin composition material to be added to a pulverized product
for recycling a recycle material containing ordinary EVOH.
RELATED ART DOCUMENT
Patent Document
[0007] PTL 1: JP-A-2000-312538 [0008] PTL 2: JP-A-2011-46929 [0009]
PTL 3: JP-A-2002-234971
SUMMARY
[0010] The resin compositions each containing the higher ethylene
content EVOH as disclosed in PTL 1 to PTL 3 are liable to be
thermally deteriorated and colored after heating in melt kneading
and melt forming. Therefore, improvement is required.
[0011] The inventors conducted intensive studies in view of the
foregoing and, as a result, found that, where the resin composition
containing the ordinary EVOH and the higher ethylene content EVOH
further contains a specific very small amount of a sorbic acid
ester, the above problem can be solved.
[0012] According to a first aspect of the present disclosure, there
is provided a resin composition containing: (A) an EVOH having an
ethylene content of 20 to 60 mol % (hereinafter referred to as
"EVOH (A)"); (B) a higher ethylene content EVOH; and (C) a sorbic
acid ester; wherein the sorbic acid ester (C) is present in an
amount of 0.00001 to 10 ppm based on the weight of the resin
composition. According to a second aspect of the present
disclosure, a melt-forming material formed from the resin
composition is provided. According to a third aspect of the present
disclosure, a multilayer structure including a layer formed from
the resin composition is provided. According to a fourth aspect of
the present disclosure, an agricultural film formed from the
multilayer structure is provided.
[0013] The resin composition of the present disclosure contains the
EVOH (A), the higher ethylene content EVOH (B), and the sorbic acid
ester (C). In the resin composition, the sorbic acid ester (C) is
present in an amount of 0.00001 to 10 ppm based on the weight of
the resin composition. Thus, the resin composition containing the
EVOH (A) and the higher ethylene content EVOH (B) is excellent in
coloration-suppressing effect for suppressing heat coloration
during melt kneading and melt forming.
[0014] Where the weight ratio of the EVOH (A) to the higher
ethylene content EVOH (B) is (A)/(B)=1/99 to 99/1, the
coloration-suppressing effect is further improved.
[0015] The melt-forming material formed from the resin composition
of the present disclosure is less susceptible to the heat
coloration and, therefore, is formed into various products, which
can be advantageously used as packaging materials, for example, for
foods, chemical agents, agricultural chemicals, and the like, and
as agricultural film materials for silage films, soil-covering
films, and the like.
[0016] The multilayer structure including the layer formed from the
resin composition of the present disclosure is highly tough and
less susceptible to heat coloration and, therefore, is formed into
various products, which can be advantageously used as packaging
materials, for example, for foods, chemical agents, agricultural
chemicals, and the like, and as agricultural films such as silage
films and soil-covering films.
DESCRIPTION OF EMBODIMENTS
[0017] Preferred embodiments of the present disclosure will
hereinafter be described in detail. It should be understood that
these preferred embodiments are illustrative but not
limitative.
[0018] <Resin Composition>
[0019] The resin composition of the present disclosure contains:
(A) an EVOH; (B) a higher ethylene content EVOH; and (C) a sorbic
acid ester. The components of the resin composition of the present
disclosure will hereinafter be described in turn.
[0020] [EVOH (A)]
[0021] The EVOH (A) to be used in the present disclosure is a
water-insoluble thermoplastic resin that is typically prepared by
copolymerizing ethylene and a vinyl ester monomer and then
saponifying the resulting copolymer, and is generally referred to
as ethylene-vinyl alcohol copolymer or saponified ethylene-vinyl
ester copolymer. A known polymerization method such as solution
polymerization method, suspension polymerization method or emulsion
polymerization method may be utilized for the polymerization. In
general, a solution polymerization method using methanol as a
solvent is utilized. The saponification of the resulting
ethylene-vinyl ester copolymer may be achieved by a known
method.
[0022] The EVOH (A) to be used in the present disclosure mainly
contains an ethylene structural unit and a vinyl alcohol structural
unit, and generally further contains a small amount of a vinyl
ester structural unit left unsaponified.
[0023] Vinyl acetate is typically used as the vinyl ester monomer,
because it is easily commercially available and ensures a higher
impurity treatment efficiency in the preparation. Other examples of
the vinyl ester monomer include aliphatic vinyl esters such as
vinyl formate, vinyl propionate, vinyl valerate, vinyl butyrate,
vinyl isobutyrate, vinyl pivalate, vinyl caprate, vinyl laurate,
vinyl stearate, and vinyl versatate, and aromatic vinyl esters such
as vinyl benzoate. The aliphatic vinyl esters preferably have a
carbon number of 3 to 20, more preferably 4 to 10, particularly
preferably 4 to 7. These vinyl esters are typically each used alone
or, as required, a plurality of vinyl esters may be selected from
these vinyl esters to be used in combination.
[0024] The ethylene content of the EVOH (A), which is measured in
conformity with ISO14663, is typically 20 to 60 mol %, preferably
25 to 50 mol %, particularly preferably 25 to 45 mol %. If the
ethylene content is excessively low, the high-humidity gas barrier
property of the thermoplastic resin and the melt formability of the
thermoplastic resin tend to be deteriorated. If the ethylene
content is excessively high, on the other hand, the gas barrier
property tends to be deteriorated.
[0025] The vinyl ester saponification degree of the EVOH (A), which
is measured in conformity with JIS K6726 (with the use of a
solution obtained by homogeneously dissolving the EVOH in a
water/methanol solvent), is typically 90 to 100 mol %, preferably
95 to 100 mol %, particularly preferably 99 to 100 mol %. If the
saponification degree is excessively low, the gas barrier property,
the heat stability, the humidity resistance, and the like tend to
be deteriorated.
[0026] The EVOH (A) typically has a melt flow rate (MFR) of 0.5 to
100 g/10 minutes, preferably 1 to 50 g/10 minutes, particularly
preferably 3 to 35 g/10 minutes (as measured at 210.degree. C. with
a load of 2160 g). If the MFR of the EVOH (A) is excessively high,
the film formability tends to be deteriorated. If the MFR of the
EVOH (A) is excessively low, the melt extrusion tends to be
difficult.
[0027] The EVOH (A) to be used in the present disclosure may
further contain a structural unit derived from any of the following
exemplary comonomers in an amount that does not impair the effects
of the present disclosure (e.g., typically in an amount of not
greater than 20 mol %, preferably not greater than 10 mol %, of the
EVOH (A)).
[0028] The comonomers include: olefins such as propylene, 1-butene,
and isobutene; hydroxyl-containing .alpha.-olefins such as
2-propen-1-ol, 3-buten-1-ol, 4-penten-1-ol, 5-hexen-1-ol,
3,4-dihydroxy-1-butene, and 5-hexene-1,2-diol, and derivatives
including esterification products (acylation products) of these
hydroxyl-containing .alpha.-olefins such as 3,4-diacyloxy-1-butene,
3,4-diacetoxy-1-butene, 2,3-diacetoxy-1-allyloxypropane,
2-acetoxy-1-allyloxy-3-hydroxypropane,
3-acetoxy-1-allyloxy-2-hydroxypropane, glycerin monovinyl ether,
and glycerin monoisopropenyl ether; hydroxymethyl vinylidenes such
as 1,3-hydroxy-2-methylenepropane and
1,5-hydroxy-3-methylenepentane, and esterification products of
these hydroxymethyl vinylidenes (i.e., vinylidene diacetates) such
as 1,3-diacetoxy-2-methylenepropane,
1,3-dipropionyloxy-2-methylenepropane, and
1,3-dibutyronyloxy-2-methylenepropane; unsaturated acids such as
acrylic acid, methacrylic acid, crotonic acid, phthalic acid
(anhydride), maleic acid (anhydride), and itaconic acid
(anhydride), salts of these unsaturated acids, and monoalkyl and
dialkyl esters of these unsaturated acids each including a C1 to
C18 alkyl group; acrylamide compounds such as acrylamide,
N-alkylacrylamides each including a C1 to C18 alkyl group,
N,N-dimethylacrylamide, 2-acrylamidopropane sulfonic acid and its
salts, and acrylamidopropyldimethylamine and its acid salts and
quaternary salts; methacrylamide compounds such as methacrylamide,
N-alkylmethacrylamides each including a C1 to C18 alkyl group,
N,N-dimethylmethacrylamide, 2-methacrylamidopropane sulfonic acid
and its salts, and methacrylamidopropyldimethylamine and its acid
salts and quaternary salts; N-vinylamides such as
N-vinylpyrrolidone, N-vinylformamide, and N-vinylacetamide; vinyl
cyanates such as acrylonitrile and methacrylonitrile; vinyl ethers
each including a C1 to C18 alkyl group such as alkyl vinyl ethers,
hydroxyalkyl vinyl ethers, and alkoxyalkyl vinyl ethers;
halogenated vinyl compounds such as vinyl chloride, vinylidene
chloride, vinyl fluoride, vinylidene fluoride, and vinyl bromide;
vinylsilanes such as trimethoxyvinylsilane; allyl acetate, and
halogenated allyl compounds such as allyl chloride; allyl alcohol
compounds such as allyl alcohol and dimethoxyallyl alcohol; and
trimethyl (3-acrylamido-3-dimethylpropyl) ammonium chloride and
acrylamido-2-methylpropane sulfonic acid. These may be used alone
or in combination.
[0029] An EVOH containing a structural unit having a primary
hydroxyl group in its side chain among structural units derived
from the aforementioned comonomers is preferred because the
secondary formability is improved in stretching process, vacuum
pressure forming process, and the like. Particularly, an EVOH
containing a structural unit having 1,2-diol in its side chain is
preferred.
[0030] Where the EVOH (A) contains the structural unit having the
primary hydroxyl group in its side chain, the primary hydroxyl
group content is typically 0.1 to 20 mol %, preferably 0.1 to 15
mol %, particularly preferably 0.1 to 10 mol %.
[0031] The EVOH (A) may be a mixture of different EVOHs. These
EVOHs may have different contents of the ethylene structural unit,
different contents of the structural unit having the primary
hydroxyl group in the side chain, different saponification degrees,
and different melt flow rates (MFRs), and contain different
comonomer components.
[0032] In the present disclosure, post-modified EVOHs such as
urethanized EVOH, acetalized EVOH, cyanoethylated EVOH, and
oxyalkylenated EVOH are also usable as the EVOH (A).
[0033] In the resin composition of the present disclosure, the EVOH
(A) is typically present in a proportion of not less than 1 wt. %,
preferably not less than 50 wt. %, more preferably not less than 60
wt. %, still more preferably not less than 70 wt. %. The upper
limit of the proportion of the EVOH (A) is typically 99 wt. %.
Where the proportion of the EVOH (A) falls within the
aforementioned ranges, the effects of the present disclosure tend
to be efficiently provided.
[0034] [Higher Ethylene Content EVOH (B)]
[0035] The higher ethylene content EVOH (B) to be used in the
present disclosure is an EVOH prepared by saponifying a vinyl
acetate component of an ethylene-vinyl acetate copolymer having an
ethylene content of not less than 70 mol % and, therefore, has a
significantly different ethylene content from the EVOH (A). The
higher ethylene content EVOH (B) is poorer in gas barrier property
than ordinary EVOH and, therefore, is generally regarded as a
thermoplastic resin different from ordinary EVOH.
[0036] The higher ethylene content EVOH (B) to be used in the
present disclosure is required to have an ethylene content of not
less than 70 mol % as measured in conformity with ISO14663, and the
upper limit of the ethylene content is typically 98 mol %. The
ethylene content of the higher ethylene content EVOH (B) is
preferably 75 to 95 mol %, more preferably 80 to 95 mol %. If the
ethylene content is excessively low, the EVOH property-improving
effect (for improving the thrust strength and the tensile
elongation of the EVOH (A)) tends to be reduced.
[0037] The higher ethylene content EVOH (B) typically has a
saponification degree of not lower than 20 mol %, preferably 40 to
100 mol %, particularly preferably 80 to 100 mol %, as measured in
conformity with JIS K6726. If the saponification degree is
excessively low, the higher ethylene content EVOH (B) tends to have
insufficient affinity for the EVOH (A) and poorer dispersibility.
Therefore, the film appearance tends to be deteriorated, and the
thrust strength-improving effect and the tensile
elongation-improving effect tend to be reduced.
[0038] The higher ethylene content EVOH (B) typically has a melt
flow rate (MFR) of 0.5 to 100 g/10 minutes, preferably 1 to 50 g/10
minutes, more preferably 2 to 30 g/10 minutes (as measured at
190.degree. C. with a load of 2160 g). In this case, the higher
ethylene content EVOH (B) is excellent in dispersibility to provide
excellent effects of the present disclosure.
[0039] The higher ethylene content EVOH (B) typically has a density
of 500 to 1,500 kg/m.sup.3, preferably 800 to 1,200 kg/m.sup.3,
particularly preferably 900 to 1,100 kg/m.sup.3.
[0040] The higher ethylene content EVOH (B) is prepared by
polymerizing ethylene and vinyl acetate by a known polymerization
method such as solution polymerization method, suspension
polymerization method or emulsion polymerization method, and
saponifying the resulting copolymer by a known saponification
method. The higher ethylene content EVOH (B) may contain a
structural unit derived from any of the comonomers described above
for the EVOH (A) in an amount that does not impair the effects of
the present disclosure (e.g., in an amount of not greater than 20
mol % of the higher ethylene content EVOH (B)).
[0041] The higher ethylene content EVOH (B) may be a
carboxyl-containing carboxyl-modified higher ethylene content EVOH
obtained by chemically bonding an unsaturated carboxylic acid or
its anhydride to a higher ethylene content EVOH by an addition
reaction, a graft reaction or the like. Specifically, the
carboxyl-containing carboxyl-modified higher ethylene content EVOH
preferably has a modification degree of not higher than 10 mol %,
for example.
[0042] Examples of the unsaturated carboxylic acid and its
anhydride include: ethylenically unsaturated monocarboxylic acids
such as acrylic acid, methacrylic acid, ethacrylic acid, and
crotonic acid; and ethylenically unsaturated dicarboxylic acids,
and their anhydrides and half esters such as fumaric acid, itaconic
acid, citraconic acid, maleic acid, monomethyl maleate, monoethyl
maleate, and maleic anhydride. Of these, maleic anhydride is
preferably used.
[0043] A single higher ethylene content EVOH may be used as the
higher ethylene content EVOH (B), or two or more higher ethylene
content EVOHs having different ethylene contents, different
saponification degrees, different molecular weights, different
MFRs, different densities, different modifying groups, and/or
different modification degrees may be used as the higher ethylene
content EVOH (B).
[0044] In the resin composition of the present disclosure, the
blend weight ratio of the EVOH (A) to the higher ethylene content
EVOH (B) is typically (A)/(B)=1/99 to 99/1, preferably 50/50 to
99/1, preferably 60/40 to 99/1, more preferably 70/30 to 99/1,
still more preferably 72/28 to 95/5, particularly preferably 75/25
to 90/10, especially preferably 75/25 to 85/15. Where the blend
weight ratio of the EVOH (A) to the higher ethylene content EVOH
(B) falls within the aforementioned ranges, the
coloration-suppressing effect is further improved.
[0045] The total amount of the EVOH (A) and the higher ethylene
content EVOH (B) contained in the resin composition of the present
disclosure is typically not less than 70 wt. %, preferably not less
than 80 wt. %, more preferably not less than 90 wt. %. The upper
limit of the total amount of the EVOH (A) and the higher ethylene
content EVOH (B) corresponds to a weight obtained by subtracting
the weight of the sorbic acid ester (C) from the weight of the
resin composition.
[0046] [Sorbic Acid Ester (C)]
[0047] In the present disclosure, the resin composition containing
the EVOH (A) and the higher ethylene content EVOH (B) further
contains the sorbic acid ester (C) in a specific very small amount,
thereby providing a remarkable effect for suppressing the heat
coloration.
[0048] In a resin composition prepared by mixing the ordinary EVOH
and the higher ethylene content EVOH, the ordinary EVOH having a
lower ethylene content is generally susceptible to thermal
degradation. Therefore, it is supposed that the resin composition
has portions susceptible to degradation and portions less
susceptible to degradation.
[0049] In the present disclosure, a reason why the coloration of
the resin composition is suppressed by the blending of the specific
very small amount of the sorbic acid ester (C) is supposedly that
the sorbic acid ester (C) has a lower polarity and, therefore, can
be homogeneously dispersed in the resin composition even if being
present in the very small amount in the resin composition. It is
considered that the sorbic acid ester (C) is hydrolyzed to generate
sorbic acid, which in turn captures radicals, whereby the excellent
coloration-suppressing effect is provided. Further, it is supposed
that a so-called catalytic cycle occurs in which an alcohol
resulting from the hydrolysis of the sorbic acid ester (C) reacts
with sorbic acid capturing the radicals, whereby the sorbic acid
ester (C) is generated, and then the sorbic acid ester (C) thus
generated is thermally hydrolyzed again.
[0050] It is supposed that sorbic acid capable of capturing the
radicals thus constantly occurs and, therefore, the radicals can be
captured in the resin composition at the early stage of the radical
generation, making it possible to provide the excellent
coloration-suppressing effect. It is also supposed that, in the
present disclosure in which the resin composition contains the
sorbic acid ester (C) in the specific very small amount, the
aforementioned cycle can efficiently work to thereby provide the
remarkable coloration-suppressing effect.
[0051] A sorbic acid ester prepared by condensation of sorbic acid
and an alcohol or a phenol derivative, for example, is usable as
the sorbic acid ester (C). Specific examples of the sorbic acid
ester include alkyl sorbates such as methyl sorbate, ethyl sorbate,
propyl sorbate, butyl sorbate, and pentyl sorbate, and aryl
sorbates such as phenyl sorbate and naphthyl sorbate, which may be
used alone or in combination.
[0052] Where the acidity of the alcohol resulting from the
hydrolysis of the sorbic acid ester (C) is relatively low, the
resin composition is less susceptible to deterioration. Therefore,
the alkyl sorbates are preferred, and alkyl sorbates containing a
C1 to C5 alkoxy group are more preferred. Alkyl sorbates containing
a C1 to C3 alkoxy group are particularly preferred, and methyl
sorbate and ethyl sorbate are most preferred.
[0053] The sorbic acid ester (C) typically has a molecular weight
of 120 to 220, preferably 120 to 200, particularly preferably 120
to 160. Where the molecular weight of the sorbic acid ester (C)
falls within the aforementioned ranges, the coloration-suppressing
effect tends to be efficiently provided.
[0054] The amount of the sorbic acid ester (C) contained in the
resin composition is 0.00001 to 10 ppm, preferably 0.00005 to 5
ppm, more preferably 0.0001 to 3 ppm, particularly preferably
0.0005 to 0.5 ppm, especially preferably 0.001 to 0.1 ppm, based on
the weight of the resin composition. Where the amount of the sorbic
acid ester (C) falls within the aforementioned ranges, the
coloration-suppressing effect is improved. If the amount of the
sorbic acid ester (C) is excessively great, the number of
conjugated double bonds is excessively great, so that the
coloration is liable to result.
[0055] The amount of the sorbic acid ester (C) contained in the
resin composition is typically 0.0001 to 10 ppm, preferably 0.0003
to 5 ppm, more preferably 0.0005 to 3 ppm, particularly preferably
0.0008 to 1 ppm, especially preferably 0.001 to 0.5 ppm, based on
the total weight of the EVOH (A) and the sorbic acid ester (C).
Where the amount of the sorbic acid ester (C) falls within the
aforementioned ranges, the coloration-suppressing effect is
efficiently provided. If the amount of the sorbic acid ester (C) is
excessively great, the number of conjugated double bonds is
excessively great, so that the coloration is liable to result.
[0056] In the case of pellets and other products formed from the
resin composition of the present disclosure, the amount of the
sorbic acid ester (C) contained in the resin composition can be
measured by the following method. A sample is first prepared by
pulverizing the formed product (e.g., the pellets) by a given
method (e.g., a freeze-pulverizing method), and dissolving the
pulverized product in a C1 to C5 lower alcohol solvent. Then, the
sample is analyzed by a liquid chromatography/mass spectrometry
(LC/MS/MS) method, whereby the amount of the sorbic acid ester (C)
is determined.
[0057] In the case of a formed product containing the resin
composition and some other thermoplastic resin or the like (e.g., a
multilayer structure), a layer of the resin composition to be
analyzed is taken out of the multilayer structure by a given
method, and the measurement is performed in the aforementioned
manner.
[0058] [Carboxyl-Containing Ethylene-Vinyl Acetate Copolymer]
[0059] In the present disclosure, a carboxyl-containing
ethylene-vinyl acetate copolymer (hereinafter referred to as
"acid-modified EVA") is preferably used to compatibilize the EVOH
(A) and the higher ethylene content EVOH (B) to homogeneously
disperse the EVOH (A) and the higher ethylene content EVOH (B) in
the resin composition.
[0060] The acid-modified EVA is obtained by chemically bonding an
unsaturated carboxylic acid or its anhydride to an ethylene-vinyl
acetate copolymer typically having an ethylene content of not less
than 70 mol %. The acid-modified EVA, which is not subjected to the
saponification and, hence, contains no hydroxyl group, is a
completely different resin from the higher ethylene content EVOH
(B). Further, the acid-modified EVA is a completely different resin
from the EVOH (A), because it lacks the excellent gas barrier
property.
[0061] The acid-modified EVA is obtained by chemically bonding the
unsaturated carboxylic acid or its anhydride to the ethylene-vinyl
acetate copolymer by an addition reaction, a graft reaction or the
like. Examples of the unsaturated carboxylic acid and its anhydride
include maleic acid, maleic anhydride, fumaric acid, acrylic acid,
methacrylic acid, crotonic acid, itaconic acid, citraconic acid,
and hexahydrophthalic anhydride. Of these, maleic anhydride is
preferably used. Specifically, a mixture containing one or two or
more selected from polyethylenes modified with maleic anhydride,
polypropylenes modified with maleic anhydride, ethylene-propylene
copolymers modified with maleic anhydride, ethylene-methyl acrylate
copolymers modified with maleic anhydride, ethylene-ethyl acrylate
copolymers modified with maleic anhydride, and ethylene-vinyl
acetate copolymers modified with maleic anhydride is preferred.
[0062] The modification degree of the acid-modified EVA modified
with the unsaturated carboxylic acid or its anhydride is preferably
0.001 to 3 wt. %, more preferably 0.01 to 1 wt. %, particularly
preferably 0.03 to 0.5 wt. %. If the modification degree is
excessively low, it tends to be impossible to sufficiently provide
the effect of the acid-modified EVA for improving the compatibility
between the EVOH (A) and the higher ethylene content EVOH (B). If
the modification degree is excessively high, on the other hand, the
resin composition tends to be poorer in heat stability.
[0063] The acid-modified EVA typically has a melt flow rate (MFR)
of 0.5 to 100 g/10 minutes, preferably 1 to 50 g/10 minutes, more
preferably 2 to 30 g/10 minutes, as measured at 190.degree. C. with
a load of 2160 g.
[0064] The acid-modified EVA typically has a density of 500 to
1,500 kg/m.sup.3, preferably 800 to 1,200 kg/m.sup.3, more
preferably 900 to 1,000 kg/m.sup.3.
[0065] In the present disclosure, a single acid-modified EVA may be
used, or two or more acid-modified EVAs having different ethylene
contents, different molecular weights, different MFRs, different
densities, different modifying groups, and/or different
modification degrees falling within the aforementioned ranges may
be used in combination.
[0066] The amount of the acid-modified EVA contained in the resin
composition of the present disclosure is 0.1 to 10 parts by weight,
more preferably 0.5 to 8 parts by weight, particularly preferably 2
to 5 parts by weight, based on 100 parts by weight of the EVOH
(A).
[0067] In the resin composition, the blend weight ratio of the
higher ethylene content EVOH (B) to the acid-modified EVA is 1 to
400, preferably 2 to 100, more preferably 3 to 50, particularly
preferably 4 to 20.
[0068] [Other Thermoplastic Resin]
[0069] The resin composition of the present disclosure may further
contain a thermoplastic resin other than the EVOH (A), the higher
ethylene content EVOH (B), and the acid-modified EVA as a resin
component in an amount that does not impair the effects of the
present disclosure (typically in an amount of not greater than 30
wt. %, preferably not greater than 10 wt. %, more preferably not
greater than 5 wt. %, particularly preferably not greater than 3
wt. %, based on the weight of the resin composition).
[0070] Specific examples of the other thermoplastic resin include
olefin homopolymers and copolymers such as linear low-density
polyethylenes, low-density polyethylenes, medium-density
polyethylenes, high-density polyethylenes, ethylene-vinyl acetate
copolymers, ionomers, ethylene-propylene copolymers,
ethylene-.alpha.-olefin (C4 to C20 .alpha.-olefin) copolymers,
ethylene-acrylate copolymers, polypropylenes,
propylene-.alpha.-olefin (C4 to C20 .alpha.-olefin) copolymers,
polybutenes, and polypentenes, polycycloolefins, polyolefin resins
in a broader sense such as modified polyolefin resins obtained by
graft-modifying any of the aforementioned olefin homopolymers and
copolymers with an unsaturated carboxylic acid or an unsaturated
carboxylic acid ester, polystyrene resins, polyester resins,
chlorinated vinyl resins such as polyvinyl chlorides and
polyvinylidene chlorides, polyamide resins, acrylic resins, vinyl
ester resins, polystyrene elastomers, polyester elastomers,
polyurethane elastomers, chlorinated polyethylenes, and chlorinated
polypropylenes. These thermoplastic resins may be used alone or in
combination.
[0071] [Other Additives]
[0072] As required, the resin composition of the present disclosure
may contain known additives in addition to the aforementioned
components in amounts that do not impair the effects of the present
disclosure (e.g., typically in amounts of not greater than 10 wt.
%, preferably not greater than 5 wt. %, particularly preferably not
greater than 3 wt. %, based on the overall weight of the resin
composition). Examples of the additives include: plasticizer (e.g.,
aliphatic polyhydric alcohol such as ethylene glycol, glycerin,
hexanediol, or the like); lubricant such as higher fatty acid
(e.g., lauric acid, myristic acid, palmitic acid, stearic acid,
behenic acid, oleic acid, or the like), higher fatty acid metal
salt (e.g., calcium stearate, magnesium stearate, or the like),
higher fatty acid ester (e.g., methyl ester, isopropyl ester, butyl
ester, octyl ester, or the like of higher fatty acid), higher fatty
acid amide (e.g., stearamide, oleamide, or the like), bis-higher
fatty acid amide (e.g., ethylene bis-stearamide, or the like), or
low-molecular weight polyolefin (e.g., low-molecular weight
polyethylene or low-molecular weight polypropylene having a
molecular weight of about 500 to about 10,000); drying agent;
oxygen absorber; heat stabilizer; photo stabilizer; flame
retardant; crosslinking agent; curing agent; foaming agent; crystal
nucleating agent; antifogging agent; biodegradation agent; silane
coupling agent; antiblocking agent; antioxidant; colorant;
antistatic agent; UV absorber; antibacterial agent; insoluble
inorganic double salt (e.g., hydrotalcites or the like);
surfactant; and wax. These may be used alone or in combination.
[0073] Examples of the heat stabilizer to be used for improving the
heat stability and other various physical properties during the
melt forming include: organic acids such as acetic acid, propionic
acid, and butyric acid, salts of the organic acids such as alkali
metal salts (sodium salts, potassium salts, and the like), alkali
earth metal salts (calcium salts, magnesium salts, and the like),
and zinc salts of the organic acids; and inorganic acids such as
sulfuric acid, sulfurous acid, carbonic acid, phosphoric acid, and
boric acid, and alkali metal salts (sodium salts, potassium salts,
and the like), alkali earth metal salts (calcium salts, magnesium
salts, and the like), and zinc salts of the inorganic acids.
[0074] Of these, acetic acid, boron compounds such as boric acid
and its salts, acetic acid salts, and phosphoric acid salts are
preferably blended as the heat stabilizer.
[0075] The amount of acetic acid to be blended as the heat
stabilizer is typically 0.001 to 1 part by weight, preferably 0.005
to 0.2 parts by weight, particularly preferably 0.01 to 0.1 part by
weight, based on 100 parts by weight of the EVOH (A). If the amount
of acetic acid is excessively small, the effect of blending acetic
acid tends to be reduced. If the amount of acetic acid is
excessively great, on the other hand, formation of a uniform film
tends to be difficult.
[0076] The amount of a boron compound to be blended as the heat
stabilizer is typically 0.001 to 1 part by weight on a boron basis
based on 100 parts by weight of the EVOH (A) (as measured by ICP
emission spectrometry after ashing). If the amount of the boron
compound is excessively small, the effect of blending the boron
compound tends to be reduced. If the amount of the boron compound
is excessively great, on the other hand, formation of a uniform
film tends to be difficult.
[0077] The amount of an acetic acid salt or a phosphoric acid salt
(or a hydrogen phosphoric acid salt) to be blended as the heat
stabilizer is typically 0.0005 to 0.1 part by weight on a metal
basis based on 100 parts by weight of the EVOH (A) (as measured by
ICP emission spectrometry after ashing). If the amount of the
acetic acid salt or the phosphoric acid salt is excessively small,
the effect of the blending tends to be reduced. If the amount of
the acetic acid salt or the phosphoric acid salt is excessively
great, on the other hand, formation of a uniform film tends to be
difficult. Where two or more salts are blended in the resin
composition, the total amount of the two or more salts preferably
falls within the aforementioned ranges.
[0078] [Resin Composition Production Method]
[0079] The resin composition of the present disclosure is produced
by using the EVOH (A), the higher ethylene content EVOH (B), and
the sorbic acid ester (C) as the essential components and, as
required, using the acid-modified EVA and any of the aforementioned
optional additives. Known examples of a method for the production
include dry blending method, melt mixing method, solution mixing
method, and impregnation method, which may be used in
combination.
[0080] An example of the dry blending method is a method (I)
including the step of dry-blending the sorbic acid ester (C) with
pellets containing at least one selected from the group consisting
of the EVOH (A) and the higher ethylene content EVOH (B) by means
of a tumbler or the like.
[0081] Examples of the melt mixing method include: a method (II)
including the steps of melt-kneading a dry blend of the sorbic acid
ester (C) and pellets containing at least one selected from the
group consisting of the EVOH (A) and the higher ethylene content
EVOH (B), and forming the resulting melt mixture into pellets or
other product; and a method (III) including the steps of adding the
sorbic acid ester (C) to at least one selected from the group
consisting of the EVOH (A) and the higher ethylene content EVOH (B)
in a melted state, melt-kneading the resulting mixture, and forming
the resulting melt mixture into pellets or other product.
[0082] Examples of the solution mixing method include: a method
(IV) including the steps of preparing a solution by using
commercially available pellets containing at least one selected
from the group consisting of the EVOH (A) and the higher ethylene
content EVOH (B), blending the sorbic acid ester (C) with the
solution, solidifying and forming the resulting solution into
pellets, separating the pellets from the solution, and drying the
pellets; and a method (V) including the steps of adding at least
one selected from the group consisting of the sorbic acid ester (C)
and a solution of the higher ethylene content EVOH (B) to a
homogeneous solution (water/alcohol solution or the like) of the
EVOH after the saponification in the preparation of the EVOH (A),
solidifying and forming the resulting solution into pellets,
separating the pellets from the solution, and drying the
pellets.
[0083] An example of the impregnation method is a method (VI)
including the steps of bringing pellets containing at least one
selected from the group consisting of the EVOH (A) and the higher
ethylene content EVOH (B) into contact with an aqueous solution
containing the sorbic acid ester (C) to incorporate the sorbic acid
ester (C) into the pellets, and then drying the resulting
pellets.
[0084] In the methods described above, a composition (master batch)
containing the sorbic acid ester (C) at a higher concentration may
be prepared by blending the sorbic acid ester (C) in a
predetermined proportion with at least one selected from the group
consisting of the EVOH (A) and the higher ethylene content EVOH
(B), and the resin composition may be produced as containing the
sorbic acid ester (C) at a predetermined concentration by blending
the master batch with the EVOH (A) or the higher ethylene content
EVOH (B).
[0085] In the present disclosure, different methods may be selected
from the aforementioned methods to be used in combination.
Particularly, the melt mixing method is preferred, and the method
(II) is particularly preferred, because the resin composition
produced by these methods is significantly improved in productivity
and the effects of the present disclosure.
[0086] Where the acid-modified EVA and any of the aforementioned
additives are blended as optional components in the resin
composition, the aforementioned production methods may be employed
in substantially the same manner for blending the optional
components in the resin composition.
[0087] Pellets of the resin composition to be produced by any of
the aforementioned methods, and the pellets containing at least one
selected from the group consisting of the EVOH (A) and the higher
ethylene content EVOH (B) to be used in any of the aforementioned
methods may each have any desired shape. The pellets may each have,
for example, spherical shape, oval shape, cylindrical shape, cubic
shape, square prism shape, or the like, and typically the oval
shape or the cylindrical shape. For easy handling of the pellets in
the subsequent use as a forming material, the cylindrical pellets
typically each have a bottom diameter of 1 to 6 mm and a length of
1 to 6 mm, preferably a bottom diameter of 2 to 5 mm and a length
of 2 to 5 mm. In the case of the oval pellets, the major diameter
is typically 1.5 to 30 mm, preferably 3 to 20 mm, more preferably
3.5 to 10 mm, and the minor diameter is typically 1 to 10 mm,
preferably 2 to 6 mm, particularly preferably 2.5 to 5.5 mm. In an
exemplary method for determination of the major diameter and the
minor diameter, a pellet is observed on a hand, and the major
diameter of the pellet is measured by means of a measuring
instrument such as a caliper. Then, a maximum sectional plane
orthogonal to the major diameter is visually and tactually
identified, and the minor diameter of the maximum sectional plane
is measured in the aforementioned manner.
[0088] The resin composition of the present disclosure typically
has a water content of 0.01 to 0.5 wt. %, preferably 0.05 to 0.35
wt. %, particularly preferably 0.1 to 0.3 wt. %.
[0089] In the present disclosure, the water content of the resin
composition is measured and calculated by the following method.
[0090] The weight (W1) of a sample of the resin composition is
measured at a room temperature (25.degree. C.) by an electronic
balance before drying, and the sample is dried at 150.degree. C.
for 5 hours in a hot air dryer. After drying, the sample is cooled
in a desiccator for 30 minutes. After the temperature of the sample
of the resin composition is returned to the room temperature
(25.degree. C.), the weight (W2) of the sample is measured. The
water content of the resin composition is calculated from the
following expression:
Water content (wt. %)=[(W1-W2)/W1].times.100
[0091] The resin composition of the present disclosure may be
produced in any of various forms, e.g., in pellet form, powdery
form, or liquid form, for use as a forming material for various
formed products. Particularly, the resin composition of the present
disclosure is preferably provided as a melt forming material,
because the effects of the present disclosure tend to be more
efficiently provided. The resin composition of the present
disclosure may be a resin composition prepared by mixing the resin
composition with a resin other than the EVOH (A) and the higher
ethylene content EVOH (B).
[0092] The pellets of the resin composition of the present
disclosure may be used as they are for the melt forming. In order
to ensure stable feeding of the resin composition pellets in the
melt forming, it is also preferred to apply a known lubricant to
surfaces of the pellets. Any of the lubricants described above may
be used. The amount of the lubricant present on the pellets is
typically not greater than 5 wt. %, preferably not greater than 1
wt. %, based on the weight of the resin composition.
[0093] Exemplary products to be formed from the resin composition
of the present disclosure for practical applications include a
single-layer film formed by using the resin composition of the
present disclosure, and a multilayer structure including a layer
formed by using the resin composition of the present
disclosure.
[0094] [Multilayer Structure]
[0095] A multilayer structure of the present disclosure includes a
layer formed from the resin composition of the present disclosure.
The layer formed from the resin composition of the present
disclosure (hereinafter referred to as "resin composition layer")
may be laminated with some other base material (hereinafter
referred to as "base resin") containing a thermoplastic resin other
than the resin composition of the present disclosure as a major
component. Thus, the resin composition layer can be strengthened,
protected from moisture and other influence, and/or imparted with
an additional function.
[0096] Examples of the base resin include: (unmodified) polyolefin
resins including polyethylene resins such as linear low-density
polyethylenes, low-density polyethylenes, very-low-density
polyethylenes, medium-density polyethylenes, high-density
polyethylenes, ethylene-propylene (block and random) copolymers,
and ethylene-.alpha.-olefin (C4 to C20 .alpha.-olefin) copolymers,
polypropylene resins such as polypropylenes and
propylene-.alpha.-olefin (C4 to C20 .alpha.-olefin) copolymers,
polybutenes, polypentenes, and polycycloolefin resins (polymers
having a cycloolefin structure in a main chain and/or a side chain
thereof); polyolefin resins in a broader sense including modified
olefin resins such as unsaturated carboxyl-modified polyolefin
resins obtained by graft-modifying any of the aforementioned
polyolefin resins with an unsaturated carboxylic acid or an
unsaturated carboxylic acid ester; and ionomers, ethylene-vinyl
acetate copolymers, ethylene-acrylic acid copolymers,
ethylene-acrylate copolymers, polyester resins, polyamide resins
(including polyamide copolymers), polyvinyl chlorides,
polyvinylidene chlorides, acrylic resins, polystyrene resins, vinyl
ester resins, polyester elastomers, polyurethane elastomers,
polystyrene elastomers, halogenated polyolefins such as chlorinated
polyethylenes and chlorinated polypropylenes, and aromatic and
aliphatic polyketones. These may be used alone or in
combination.
[0097] Of these, the polyamide resins, the polyolefin resins, the
polyester resins, and the polystyrene resins, which are hydrophobic
resins, are preferred, and the polyolefin resins such as the
polyethylene resins, the polypropylene resins, the polycycloolefin
resins, and the unsaturated carboxyl-modified polyolefin resins
obtained by modifying these polyolefin resins are more preferred.
Particularly, the polycycloolefin resins are preferred as
hydrophobic resins.
[0098] Where layers a (a1, a2, . . . ) formed from the resin
composition of the present disclosure and base resin layers b (b1,
b2, . . . ) are laminated together to produce a multilayer
structure, the layered configuration of the multilayer structure
may be any combination of these layers, e.g., a/b, b/a/b, a/b/a,
a1/a2/b, a/b1/b2, b2/b1/a/b1/b2, b2/b1/a/b1/a/b1/b2, or the like.
Where the multilayer structure further includes a recycle layer R
formed from a mixture obtained by re-melting cutoff pieces and
defective products occurring during the production of the
multilayer structure and containing the resin composition of the
present disclosure and the base resin, possible combinations of the
layers for the layered configuration include b/R/a, b/R/a/b,
b/R/a/R/b, b/a/R/a/b, b/R/a/R/a/R/b, and the like. The total number
of the layers of the multilayer structure is typically 2 to 15,
preferably 3 to 10. In the aforementioned layered configuration, as
required, an adhesive resin layer containing an adhesive resin may
be provided between the layers.
[0099] Known adhesive resins are usable as the adhesive resin. The
adhesive resin is properly selected according to the type of the
thermoplastic resin to be used for the base resin layers b. Typical
examples of the adhesive resin include carboxyl-containing modified
polyolefin polymers prepared by chemically bonding an unsaturated
carboxylic acid or its anhydride to a polyolefin resin by an
addition reaction, a graft reaction or the like. Examples of the
carboxyl-containing modified polyolefin polymers include
polyethylenes graft-modified with maleic anhydride, polypropylenes
graft-modified with maleic anhydride, ethylene-propylene (block and
random) copolymers graft-modified with maleic anhydride,
ethylene-ethyl acrylate copolymers graft-modified with maleic
anhydride, ethylene-vinyl acetate copolymers graft-modified with
maleic anhydride, polycycloolefin resins modified with maleic
anhydride, and polyolefin resins graft-modified with maleic
anhydride. These adhesive resins may be each used alone, or two or
more of these adhesive resins may be used as a mixture.
[0100] Where the adhesive resin layer is provided between the resin
composition layer and the base resin layer in the multilayer
structure, the adhesive resin layer is located in contact with the
resin composition layer and, therefore, a highly hydrophobic
adhesive resin is preferably used for the adhesive resin layer.
[0101] The base resin and the adhesive resin may each contain
conventionally known plasticizer, filler, clay (montmorillonite or
the like), colorant, antioxidant, antistatic agent, lubricant,
nucleating agent, antiblocking agent, wax, and the like in amounts
that do not impair the effects of the present disclosure (e.g.,
typically in amounts of not greater than 30 wt. %, preferably not
greater than 10 wt. %, based on the weight of the base resin or the
adhesive resin). These may be used alone or in combination.
[0102] The resin composition layer formed from the resin
composition of the present disclosure and the base resin layer may
be laminated together (optionally with the adhesive resin layer
provided therebetween) by a known laminating method. Examples of
the laminating method include: a method in which a film or a sheet
of the resin composition of the present disclosure is laminated
with the base resin by melt extrusion; a method in which the base
resin layer is laminated with the resin composition of the present
disclosure by melt extrusion; a method in which the resin
composition and the base resin are coextruded; a method in which
the resin composition layer and the base resin layer are
dry-laminated together with the use of a known adhesive agent such
as of organic titanium compound, isocyanate compound, polyester
compound or polyurethane compound; and a method in which a solution
of the resin composition is applied on the base resin layer, and a
solvent is removed from the applied solution. Of these methods, the
coextrusion method is preferred from the viewpoint of costs and
environmental concerns.
[0103] The multilayer structure described above is further
subjected to a (heat) stretching process as required. The
stretching process may be a uniaxial stretching process or a
biaxial stretching process. The biaxial stretching process may be a
simultaneous stretching process or a sequential stretching process.
Exemplary methods for the stretching process include roll
stretching method, tenter stretching method, tubular stretching
method, stretch blowing method, and vacuum pressure forming method
each having a higher stretch ratio. A temperature for the
stretching is close to the melting point of the multilayer
structure, and is typically selected from a range of about
40.degree. C. to about 170.degree. C., preferably about 60.degree.
C. to about 160.degree. C. If the stretching temperature is
excessively low, the stretchability tends to be poorer. If the
stretching temperature is excessively high, it tends to be
difficult to ensure stable stretching.
[0104] The resulting multilayer structure may be further subjected
to a heat setting process to ensure dimensional stability after the
stretching. The heat setting process may be performed in a known
manner. For example, the stretched film is typically heat-treated
at 80.degree. C. to 180.degree. C., preferably 100.degree. C. to
165.degree. C., for about 2 to about 600 seconds, while being kept
tense. Where the stretched multilayer film produced by using the
resin composition of the present disclosure is used as a shrinkable
film, the stretched film may be cold-set so as to be imparted with
a heat-shrinkable property, for example, by applying cold air over
the stretched film without performing the above heat setting
process.
[0105] Further, a cup-shaped or tray-shaped multilayer container
may be produced by using the multilayer structure of the present
disclosure. In this case, a drawing process is typically employed.
Specific examples of the drawing process include vacuum forming
method, pressure forming method, vacuum pressure forming method,
and plug-assisted vacuum pressure forming method. Where a
tube-shaped or bottle-shaped multilayer container (laminate
structure) is produced from a multilayer parison (a hollow tubular
preform to be blown), a blow molding process is employed. Specific
examples of the blow molding process include extrusion blow molding
method (twin head type, mold shift type, parison shift type, rotary
type, accumulator type, horizontal parison type, and the like),
cold parison blow molding method, injection blow molding method,
and biaxial stretching blow molding method (extrusion type cold
parison biaxial stretching blow molding method, injection type cold
parison biaxial stretching blow molding method, injection inline
type biaxial stretching blow molding method, and the like). As
required, the resulting multilayer structure may be subjected to
heating process, cooling process, rolling process, printing
process, dry laminating process, solution or melt coating process,
bag forming process, deep drawing process, box forming process,
tube forming process, splitting process, or the like.
[0106] The thickness of the multilayer structure (or the stretched
multilayer structure) and the thicknesses of the resin composition
layer, the base resin layer, and the adhesive resin layer of the
multilayer structure vary depending upon the layered configuration,
the type of the base resin, the type of the adhesive resin, and the
use purpose, the package shape, the required physical properties,
and the like of the multilayer structure. The thickness of the
multilayer structure (or the stretched multilayer structure) is
typically 10 to 5,000 .mu.m, preferably 30 to 3,000 .mu.m,
particularly preferably 50 to 2,000 .mu.m. The thickness of the
resin composition layer is typically 1 to 500 .mu.m, preferably 3
to 300 .mu.m, particularly preferably 5 to 200 .mu.m. The thickness
of the base resin layer is typically 5 to 3,000 .mu.m, preferably
10 to 2,000 .mu.m, particularly preferably 20 to 1,000 .mu.m. The
thickness of the adhesive resin layer is typically 0.5 to 250
.mu.m, preferably 1 to 150 .mu.m, particularly preferably 3 to 100
.mu.m.
[0107] The thickness ratio between the resin composition layer and
the base resin layer of the multilayer structure (resin composition
layer/base resin layer) (if these layers each include a plurality
of layers, the thickness ratio between the thickest one of the
resin composition layers and the thickest one of the base resin
layers) is typically 1/99 to 50/50, preferably 5/95 to 45/55,
particularly preferably 10/90 to 40/60. The thickness ratio between
the resin composition layer and the adhesive resin layer of the
multilayer structure (resin composition layer/adhesive resin layer)
(if these layers each include a plurality of layers, the thickness
ratio between the thickest one of the resin composition layers and
the thickest one of the adhesive resin layers) is typically 10/90
to 99/1, preferably 20/80 to 95/5, particularly preferably 50/50 to
90/10.
[0108] Bags, cups, trays, tubes, bottles, and other containers, and
caps produced from the film, the sheet or the stretched film formed
in the aforementioned manner are useful as packaging materials and
packaging containers for general foods, condiments such as
mayonnaise and dressing, fermented foods such as miso, fat and oil
such as salad oil, beverages, cosmetics, pharmaceutical products,
and the like. Further, the resin composition of the present
disclosure and the multilayer structure including the layer formed
from the resin composition of the present disclosure are highly
tough and less susceptible to the coloration and, therefore, are
very useful for agricultural film materials or agricultural
films.
EXAMPLES
[0109] Embodiments of the present disclosure will hereinafter be
described more specifically by way of examples thereof. However, it
should be understood that the present disclosure be not limited to
the examples within the scope of the present disclosure.
[0110] In the following examples, "parts" and "%" are based on
weight, unless otherwise specified.
[0111] Prior to implementation of Examples, pellets of the
following EVOH (A) and higher ethylene content EVOH (B) were
prepared.
[0112] EVOH (A): Ethylene-vinyl alcohol copolymer having an
ethylene structural unit content of 29 mol %, a saponification
degree of 100 mol %, and an MFR of 3.2 g/10 minutes (as measured at
210.degree. C. with a load of 2160 g)
[0113] Higher ethylene content EVOH (B): Saponified ethylene-vinyl
acetate copolymer (MELTHENE H0051K available from Tosoh
Corporation) having an ethylene structural unit content of 89 mol
%, a saponification degree of 99 mol %, and an MFR of 6.5 g/10
minutes (as measured at 190.degree. C. with a load of 2160 g)
Example 1
[0114] First, 80 parts of the pellets of the EVOH (A) and 20 parts
of the pellets of the higher ethylene content EVOH (B) were
dry-blended. Then, 100 parts of the dry-blended pellets and
0.0000004 parts (corresponding to 0.004 ppm based on the weight of
resin composition) of methyl sorbate (available from FUJIFILM Wako
Pure Chemical Corporation, and having a molecular weight of 126) as
the sorbic acid ester (C) were pre-heated at 230.degree. C. for 5
minutes and then melt-kneaded at 230.degree. C. for 5 minutes by
operating a plastograph (available from Brabender Corporation) at
50 rpm. Then, the resulting melt mixture was cooled and solidified,
whereby a resin composition was prepared in an aggregated form. The
resin composition thus prepared was pulverized by operating a
crusher (SKR16-240 available from Sometani Sangyo Co., Ltd.) with
its rotary blade rotated at a rotation speed of 650 rpm. The
pulverized product of the resin composition was in a granular form
having a size of 1- to 5-mm square. The resin composition had a
water content of 0.20%.
Example 2
[0115] A resin composition and a pulverized product of the resin
composition of Example 2 were produced in substantially the same
manner as in Example 1, except that the amount of methyl sorbate
was 0.00008 parts (corresponding to 0.8 ppm based on the weight of
the resin composition). The resin composition had a water content
of 0.21%.
Example 3
[0116] A resin composition and a pulverized product of the resin
composition of Example 3 were produced in substantially the same
manner as in Example 1, except that ethyl sorbate (available from
FUJIFILM Wako Pure Chemical Corporation, and having a molecular
weight of 140) was used instead of methyl sorbate. The resin
composition had a water content of 0.15%.
Comparative Example 1
[0117] A resin composition and a pulverized product of the resin
composition of Comparative Example 1 were produced in substantially
the same manner as in Example 1, except that methyl sorbate was not
blended. The resin composition had a water content of 0.16%.
Comparative Example 2
[0118] A resin composition and a pulverized product of the resin
composition of Comparative Example 2 were produced in substantially
the same manner as in Example 1, except that the amount of methyl
sorbate was 0.0012 parts (corresponding to 12 ppm based on the
weight of the resin composition). The resin composition had a water
content of 0.20%.
Comparative Example 3
[0119] A pulverized product of Comparative Example 3 was produced
by the melt-kneading and the pulverization in substantially the
same manner as in Example 1, except that the higher ethylene
content EVOH (B) and the sorbic acid ester (C) were not blended but
the EVOH (A) was used alone. The EVOH (A) had a water content of
0.11%.
[0120] The resin compositions of Examples 1 to 3, and Comparative
Examples 1 to 3 were each evaluated for the coloration by the
following method. The results are shown below in Table 1.
[0121] [Coloration Evaluation]
[0122] The pulverized products of Examples 1 to 3, and Comparative
Examples 1 to 3 were each evaluated based on the area ratio
("3803"/"4076") of a colored area having Color No. 3803 (R232,
G216, B184) to a colored area having Color No. 4076 (R248, G232,
B200) measured by means of a visual analyzer IRIS VA400 (available
from Alpha mos K.K.) Color No. 3803 means a deep yellowish color,
and Color No. 4076 means a light yellowish color. A higher value of
the colored area ratio means that the resin composition was
yellowed.
TABLE-US-00001 TABLE 1 Comparative Comparative Comparative Example
1 Example 2 Example 3 Example 1 Example 2 Example 3 EVOH (A)
(parts) 80 80 80 80 80 100 Higher ethylene content 20 20 20 20 20
-- EVOH (B) (parts) Sorbic acid ester (C) Type Methyl Methyl Ethyl
-- Methyl -- sorbate sorbate sorbate sorbate Amount (ppm) 0.004 0.8
0.004 -- 12 -- Coloration evaluation 0.3 0.4 0.3 1.8 0.8 0.5
[0123] As shown in Table 1, the resin composition of Comparative
Example 1 containing the higher ethylene content EVOH (B) had a
higher coloration evaluation value than the resin of Comparative
Example 3 containing the EVOH (A) alone. This means that the resin
composition of Comparative Example 1 is more liable to be thermally
colored during melt kneading because it contains the higher
ethylene content EVOH (B). Further, the resin composition of
Comparative Example 2 in which the sorbic acid ester (C) was
contained in an amount greater than the range specified by the
present disclosure had a slightly improved coloration evaluation
result over the resin composition of Comparative Example 1. In
contrast, the resin compositions of Examples 1 to 3 each containing
a specific very small amount of the sorbic acid ester (C) each had
a significantly improved coloration evaluation result over the
resin composition of Comparative Example 1 not containing the
sorbic acid ester (C) and the resin composition of Comparative
Example 2 containing a greater amount of the sorbic acid ester (C),
and were further improved in coloration-suppressing effect compared
with the resin of Comparative Example 3 containing the EVOH (A)
alone.
[0124] The remarkable effects of the present disclosure can be
understood from these results.
[0125] Multilayer structures produced by using the resin
compositions of Examples produced in the aforementioned manner, and
agricultural films produced by using the multilayer structures are
less susceptible to the heat coloration.
[0126] While specific forms of the embodiments of the present
disclosure have been shown in the aforementioned examples, the
examples are merely illustrative but not limitative. It is
contemplated that various modifications apparent to those skilled
in the art could be made within the scope of the disclosure.
[0127] The resin composition of the present disclosure is highly
tough and less susceptible to the coloration. Therefore, the resin
composition of the present disclosure, and the multilayer structure
including the layer formed from the resin composition of the
present disclosure are useful for packaging materials and packaging
containers for various foods, condiments such as mayonnaise and
dressing, fermented foods such as miso, fat and oil such as salad
oil, beverages, cosmetics, and pharmaceutical products. Further,
the multilayer structure is very useful for an agricultural film
material and an agricultural film.
* * * * *